The present invention relates to an optical semiconductor device, such as a semiconductor laser and a light-emitting diode having a light-emitting portion and a light-receiving portion for monitoring a light output of the light-emitting portion and a method of manufacturing the optical semiconductor device.
It is customary that semiconductor laser devices, for example, positively keep a light output emitted forward from a semiconductor laser element constant by monitoring a light output from a semiconductor laser element.
FIG. 1 of the accompanying drawings shows an example of a semiconductor laser device. As shown in FIG. 1, a semiconductor laser device 5 is composed of a semiconductor laser element 1, a beam splitter 2 and a photodiode 4. In this semiconductor laser device 5, a light output from the semiconductor laser element 1 is monitored as follows. That is, the beam splitter 2 divides a light output 3 emitted forward from the semiconductor laser element 1 to provide light 3A and light 3B. The light 3A that was reflected by the beam splitter 2 radiates a radiated object (not shown). Then, the photodiode 4 receives the light 3B passed the beam splitter 2 upon monitoring.
FIG. 2 shows other example of a semiconductor laser device. As shown in FIG. 2, a semiconductor laser device 9 is composed of a semiconductor laser chip 6 formed of a first cladding layer 6A, an active layer 6B and a second cladding layer 6C and an externally-connected photodiode 8. In this semiconductor laser device 9, the externally-connected photodiode 8 detects a light output 7B emitted rearward from the semiconductor laser chip 6 which also emits a light output 7A forward.
Further, FIG. 3 shows other example of a semiconductor laser device. As shown in FIG. 3, a semiconductor laser device 11 is composed of the semiconductor laser chip 6 formed of the first cladding layer 6A, the active layer 6B and the second cladding layer 6C and a silicon sub-mount substrate 10 having a pn junction j (i.e., photodiode PD) on which the semiconductor laser chip 6 is mounted. Thus, the semiconductor laser device 11 is of the so-called LOP (laser on photodiode) structure wherein the pn junction j on the silicon sub-mount substrate 10 detects a light output 7B emitted from the rearward of the semiconductor laser chip 6. The semiconductor laser devices 5, 9 and 11 are all built in a hybrid fashion.
Furthermore, FIG. 4 shows other example of a semiconductor laser device. As shown in FIG. 4, a semiconductor laser device 17 is composed of a semiconductor substrate 13, a semiconductor laser element 14 formed of an n-type first cladding layer 14A, an active layer 14B and a p-type second cladding layer 14C and a light-receiving portion 15. In this case, in order to form the light-receiving portion 15 in a monolithic fashion, semiconductor layers forming the n-type first cladding layer 14A, the active layer 14B and the p-type second cladding layer 14C are laminated on the semiconductor substrate 13. Then, the semiconductor laser element 14 formed of the same laminated semiconductor layer and the light-receiving portion 15 opposing a resonator end face formed behind the semiconductor laser element 14 are monolithically formed by patterning. The light receiving portion 15 receives a light output 16B emitted from the rearward of the semiconductor laser element 14 thereby to keep light 16A emitted forward from the semiconductor laser element 14 constant.
The semiconductor laser devices 4 and 9 shown in FIGS. 1 and 2 need assemblies, such as the beam splitter 2 and the photodiodes 4, 8. Therefore, they cannot be miniaturized satisfactorily and also cannot be optically disposed with a high alignment accuracy.
The semiconductor laser device 11 shown in FIG. 3 can be miniaturized but cannot be optically disposed with a high alignment accuracy.
Furthermore, the semiconductor laser device 17 shown in FIG. 4 encountered with the problem such that the light 16B emitted from the semiconductor laser element 14 is received only by the thin active layer 14B of the light-receiving portion 15. Therefore, the semiconductor laser device 17 has a small light-receiving area and is very low in sensitivity.